Rolls for rolling mills



Aug. 19, 1969 P. o. STRANDELL ROLLS FOR ROLLING MILLS Filed Feb. 6, 1967 INVENTOR PEK OLOF .(TRHMDELL- l6 E P ATTORNEYS United States Patent Office 3,461,527 Patented Aug. 19, 1969 U.S. Cl. 29--123 1 Claim ABSTRACT OF THE DISCLOSURE An arrangement in working rolls for rolling mills of the type which present a roll core and a roll ring capable of being attached to the core, the roll ring being made of some hard material, such as hard metal or ceramic material. The roll ring according to the arrangement is mounted with a clearance fit on the roll core and is secured to the same by pressure means which act axially against the flat end surfaces only of the roll ring, the pressure means imparting to the roll ring the force necessary for fixing and pre-stressing the said ring so that it is capable of withstanding the rolling forces.

BACKGROUND The present invention relates to an arrangement in rolls for rolling mills of the type which present a roll core on which can be fixed a ring or sleeve of hard material having a high degree of hardness and resistance to wear.

When material passes through the rolls of a rolling mill the surface of the rolls leave a certain imprint on the surface of the rolled material, and therefore the sur face topography of the roll barrel is of considerable importance to the surface quality of the rolled product.

The surface of the rolls are subjected to considerable wear, particularly in the case of hot rolling, which in addition to impaired microgeometry also contributes to deviations in measurements. This is particularly noticeable in the case of so-called calipered rolls which are intended to give a certain configuration, determined by the groove in said roll. Worn rolls must of necessity be periodically removed from the mills for re-grinding, resulting in reduced effective production time.

The smaller the diameter of the roll and the higher the requirements placed upon the product the more frequently the rolls must be changed. In the case of rolls of relatively small dimension it is therefore economically and technically advantageous to use a high quality wear resistant material, for instance sintered carbides of hard metals, such as tungsten, tantalum, titanium, vanadium, or a ceramic material. A material possessing admirable properties in this respect is hard metal which, however, is very brittle and can only withstand low tensile stresses or bending stresses.

The object of the invention is to eliminate these deleterious stresses, by means of a special roll structure.

In accordance herewith the invention is mainly characterized in that said ring or sleeve is capable of being mounted and is mounted, respectively, With a clearance fit on a roll core, and capable of being fixed and is fixed, respectively, to the said core by means of pressure means capable of being urged axially and which are urged axially, respectively, solely against the end surface of the sleeve, the said pressure means providing the force necessary for fixing the sleeve and enabling it to take up the forces created under rolling conditions.

The invention shall be more closely described below with reference to an embodiment of the same disclosed in the accompanying drawing, further characterizing features of the invention being disclosed in conjunction therewith.

DETAILED DESCRIPTION OF INVENTION FIGURE 1 shows in perspective, partly in section, a working roll designed in accordance with the invention. The roll shown in the drawing is intended to be used in rolling mills of the type which utilize backing rolls, i.e. a rolling mill where the material is worked between two working rolls supported by backing rolls, which take up the rolling forces.

FIGURE 2 shows a section of a similar caliper roll, designed according to the invention. I

Shown in the drawing is a roll body or core 1, suitably made of tempered steel of high strength. A ring or sleeve 2 which has circular cross section, is mounted and capable of being mounted, respectively, with a clearance fit on the roll core, the ring or sleeve 2 being made of a material having a high degree of hardness and wear resistance, e.g. a suitable hard metal. Abutting each end of said sleeve 2 is a sleeve-shaped pressuremeans 3 and 4, suitably made of metal of high pressure and tensile strength, e.g. tempered steel. The outer diameter of the pressure means are preferably at least slightly larger than the diameter of the hard metal sleeve 2, the difference in diameters being shown, although in an exaggeration, at 5 on the drawing.

The end portions of the roll core 1 are provided with trunnions 6 and also with threaded portions 7, on which are tightened nut members 8 by means of which the pressure means 3 and 4 can be tightened against the ends of the hard metal sleeve 2 so that said sleeve is fixed in position axially as well as radially relative to the core 1.

In conventional rolls provided with a hard metal ring arranged on a steel roll core it has been common practice, hitherto, to shrink the hard metal ring onto the steel core and fix the same with nuts. The design according to the invention differs to the prior method in that, as indicated above, a certain clearance exists between the hard metal ring and the steel core, which serves to prevent the occurrence of critical stresses, deleterious to the hard metal ring. The hard metal sleeve is thus secured in position, according to the invention, solely by the friction created by the pressure means 3 and 4 against the ends of the hard metal sleeve.

The rolls according to the invention are primarily intended to be used for hot rolling in which the rolls become hot and consequently expand to a certain extent. Since the coefiicient of thermal expansion of the hard metal is only half of that of the steel there is a grave risk that the hard metal ring will fracture unless a certain clearance exists between the said roll core and the roll ring. The clamping force between the pressure members 3 and 4 is so high that the friction between the outer faces of the hard metal ring and the steel surfaces of the pressure means is suflicient to take up roll forces as well as torque. This is opposed to conventional structures, in which the roll forces urge the hard metal ring against the jacket surface of the core, the said jacket surface taking up the forces created during rolling.

Grooved rolls are used when rolling sections, and an example of such a roll, designed according to the inventon, provided with a groove, which in cooperation with a similar groove in a similar roll gives the workpiece a square cross section, is shown in FIGURE 2. The roll members according to FIGURE 2 are the same as those shown in FIGURE 1, with the exception of the Slightly modified hard metal sleeve 2'; presenting a profile groove 9. This groove in itself causes a substantial weakening of the hard metal sleeve and if the roll were of a conventional design the brittle hard-metal ring would easily fracture under the lateral forces which occur in the groove during rolling. In the case of the roll according to the invention the metal ring is retained under axial pressure forces which are so powerful that the lateral forces can be completely overcome.

Since the pressure means 3 and 4 according to FIG- URES 1 and 2 have a slightly larger outer diameter than the hard metal ring, the said ring does not lie against the barrel of the backing roll. This arrangement thus avoids difficulties caused by scale and also prevents the ring from fracturing under the load existing between the working roll and backing roll. Moreover when the roll is used in backing roll mills having friction driven working rolls the torque transfer is effected steel against steel, which is favourable since steel against hard metal gives essentially lower friction.

To. ensure that the position of the roll ring does not change during the rolling operation it must be fixed to the core with a comfortable safety margin. A safety factor of 8 to 10, for instance, may be necessary. With respect to the high forces which must, thus, be applied axially to the roll ring 2 or 2 it may be convenient to preheat the roll core or the complete roll, with the exception of the roll ring, prior to securing the said ring by means of nuts 8, whereby the extent to which the roll core decreases in length as it cools can be advantageously used for the purpose of obtaining the axial tightening forces.

In one example of a roll of the type shown in FIGURE 2 the roll ring was comprised of hard metal and had an outer diameter of 80 mm., and an inner diameter of 50 mm. and a length of 30 mm. The largest outer diameter of the roll core was 45 mm. and the pressure means, on opposite sides of the roll ring, had an outer diameter of 81 mm. The complete roll, with the exception of the roll ring, was made of tempered steel. The roll ring was provided with a V-shaped groove, the sides of which were at right angles to each other and had a length of 11 mm. in cross section. The roll was intended to reduce the area of an oval workpiece by 40%, forming a square section having sides of 11 mm. in cross section. The workpiece could have comprised a plain carbon steel having a carbon content of 0.15% or a high-alloyed highspeed steel. The anticipated forces on the hard metal ring reached to approximately 2 tons for the carbon steel and 6 tons for the high speed steel. An axial force, corresponding to the force necessary for stretching the roll core 3 pro mille acting against the flat side surfaces of the roll ring was required to pre-stress and fix the hard metal ring, so that it could withstand a roll force of approximately 60 tons. This axial force was obtained by preheating the steel portions of the roll to a temperature of 270 C. prior to mounting the roll ring. Since the coefficient of thermal expansion of the hard metal is half of that of steel the nuts could be easily backed off and the pressure means and hard-metal ring then removed from the roll core, subsequent to heating the complete roll to approximately 540 C., the hard metal ring and the remaining portions of the roll comprising tempered steel being well capable of withstanding this temperature.

In addition to the possibility of using the roll for hot rolling purposes, without risk of roll ring fracture, the invention also offers the advantage that the inner surface of the roll ring of hard material need not be worked. Machining of the interiorof a hard metal ring is very expensive and can absorb upwards to half the total cost of the ring. However, to facilitate the centering of the roll ring relative to the core the said ring can be provided with an internal lining of easily machined material for instance, an aluminium or copper ring lining, fitted by shrinking, the lining being easily machined at low costs so that 'a centrally positioned hole having but a small clearance to the roll core being obtained.

What is claimed is:

1. A composite roll for rolling mills comprising a cylindrical roll core having threaded portions on at least one end thereof, a sleeve of hard material having an internal diameter slightly greater than the outer diameter of said core and end surfaces perpendicular to the roll axis, axially adjustable pressure means mounted on said threaded portions to apply force only against the end surfaces of said sleeve to thereby fix said sleeve against the forces created during rolling, said roll core and pressure means being made of high pressure, high tensile strength metal, said roll core having a coefficient of linear expansion higher than that of said sleeve, said pressure means having a cylindrical outer surface the diameter of which is slightly greater than that of said sleeve.

References Cited UNITED STATES PATENTS 256,628 4/1882 Birkholz.

983,828 2/1911 Lentz 29125 1,518,836 12/1924 Casel. 2,021,913 11/1935 Fallon 2636 2,788,957 4/1957 Lindquist 263-6 3,234,769 2/1966 Bretschneider 29l 19 X BILLY J. WILHITE, Primary Examiner US. Cl. X.R. 29-132, 148.4 

